Researchers over the last 100 years have made various attempts to process pure refractory and rare earth metals and alloys by the carbothermic process. The driving force for all of these investigations has been the low cost of carbon as the reducing agent (reductant) and the simplicity of processing with no slag formation. Some success was achieved by these workers, but high purity materials were not obtained and consistently contained large amounts of carbon (usually as metallic carbides), unreduced oxides, and other interstitials.
In the manufacture of nickel metal hydride batteries, a commonly used alloy for the negative electrode [where hydrogen ions (protons) are stored as metal hydride] comprises La(Ni,Co)4.5Si0.5. The negative electrode alloy can be prepared by reacting a La-based alloy LaSi0.5 with nickel (Ni) and cobalt (Co) in direct proportions which are usually close to equal amounts of Ni and Co.
Mischmetal (MM) comprises a majority of La, Ce collectively and minor amounts of other rare earth elements depending on the source of the ore. MM also can be used in the nickel metal hydride battery electrode such that the above-described reaction using a MM-based alloy also applies for preparing MM(Ni1-xCox)Si0.5 electrode materials.
A discussion of materials for metal-hydrogen batteries is provided by T. Sakai, M. Matsuoka and C. Iwakura, “Rare Earth Intermetallics for Metal-Hydrogen Batteries,” in Handbook on the Physics and Chemistry of Rare Earths, Ed. K. A. Gschneidner, Jr. and L. Eyring, Vol. 21, Chap. 142, pp. 133-178 (1995).
There is a need to prepare La based alloys from La2O3 in a manner that is less expensive than current processes, which use calcium (Ca) as a reducing agent or which involve electrolytic reduction of LaF3 or LaCl3 to La metal with high consumption of electricity.